KEEP an eye on your other half next Monday – it’s the peak day of the year for husbands and wives to go looking for a bit on the side.

More people stray during the winter months as a way to brighten up the long dark nights, according to an affairs website.

And the number looking for an extramarital fling will soar on January 7 as couples return to work after weeks cooped up together at home. By the end of the month more than three-quarters of a million married people are expected to have joined up to affairs website IllicitEncounters.com.

That will be six per cent of Britain’s married population looking for a dalliance on one website alone.

The site’s spokeswoman Rosie Freeman-Jones said yesterday: “Christmas and New Year are times when couples spend an intensive period of time with each other and their families.

“This can be quite claustrophobic and sometimes leads to a ‘cabin fever’ situation where both feel irritated with each other and underlying problems are exacerbated.

Christmas and New Year are times when couples spend an intensive period of time with each other

The site’s spokeswoman Rosie Freeman-Jones

“January 7 is typically one of the first days back to work – and back to freedom. Spouses take this opportunity to explore all the things they couldn’t under the watchful eye of their partner. That means lots of Facebook flirting, lots of office fun and games – and record signs-ups to Illicit Encounters.”

She claimed Seasonal Affective Disorder is also to blame for more men and woman embarking on extramarital affairs at this time of year. Illicit Encounters sees on average 25 per cent higher levels of activity during the winter months compared with the rest of the year.

Ms Freeman-Jones said: “It is highly probable that men and women are signing up and engaging in extramarital relationships as a result of SAD – caused by the onset of longer nights.

“Having an affair could be an unconscious attempt to overcome those feelings, using one of the most powerful biological weapons available to them – sex.”